1. Technical Field
The present invention relates to drilling operations, and more specifically relates to a system and method for measuring thermal damage to a printed circuit board during a drilling operation.
2. Background Art
In the process of manufacturing printed circuit boards used in the electronics industry, many holes of various sizes have to be drilled through printed circuit boards to accommodate electrical interconnection of various layers of the printed circuit board and the electronic components mounted on it. Such interconnections are typically implemented with "plated through holes" (hereinafter, PTH's). As device sizes decrease and boards become more densely populated, it becomes much more challenging to drill holes with a high degree of integrity. Because hole sizes are relatively small, and multiple materials with differing properties are utilized within the circuit board, a great deal of care and precision is required during such drilling operations. Unfortunately, failures caused by thermal damage during drilling operations remain problematic because the damage is often difficult to detect and sometimes does not surface until a board failure occurs in the field. Thermal damage to epoxy resins, which hold the layers together, and copper lands, which provide electrical contact points within the circuit board, must therefore be guarded against during drilling operations of printed circuit boards.
The problem of ensuring drilled hole integrity is complicated by the fact that a typical drilling operation includes numerous variables, each of which directly affects the integrity of the drilled hole. For example, drill bit geometry, circuit board materials and feed and speed parameters all contribute to the amount of heat generated in the drilled hole. Thus, before any change can be made to one of these and many other variables, testing must be performed to ensure that the drilling process meets the performance requirements of the circuit board. In general, if too much heat is generated within the drilled hole, damage to the nearby portions of the circuit board could potentially lead to failure.
Present techniques for measuring hole quality with respect to plated-through holes (PTH's) require the time consuming step of carefully dissecting a drilled circuit board, and examining the damage around the drilled hole, typically with a microscope or the like. Such techniques are both costly and time consuming. Therefore, any time a change of process, materials or the like is required, the cost of manufacturing a printed circuit board is increased.
A related problem involves damage resulting from drill bit wear. As a drill bit deteriorates, the drilled hole precision and integrity likewise deteriorates. Unfortunately, it is difficult to determine just when it is time to change the drill bit in a drilling operation. Changing the drill bit too soon results in additional costs resulting from bit replacement, and changing the bit too late potentially results in a circuit board malfunction.
Unfortunately, until now, there has been no inexpensive, simple and accurate method of measuring drilled hole integrity in drilling operations involving printed circuit boards and other bulk materials. This method could help reduce the cost of manufacturing printed circuit boards.